Two copper balls, each weighing 20 g are kept in air 10 cm apart. If one electron from every 106 atoms is transferred from one ball to the other, the coulomb force between them is (atomic weight of copper is 63.5)

Number of atoms in given mass =2063.5×6.02×1023                                                    =18.96×1022Transfer of electron between balls =18.96×1022106                                                       =18.96×1016Hence, magnitude of charge gained by each ball.Q=18.96×1016×1.6×10−19=0.030CForce of attraction between the ballsF=9×109×(0.030)2(0.1)2=8.1×108N